This invention relates to a logging sonde and a method of using it to define the shape of a vertical formation in the earth.
Very steep or substantially vertical boundaries are found in the earth, such as on the flanks of salt domes or igneous intrusions. Determining the boundaries of such formations is difficult. Conventional seismic exploration from the surface provides good definition of horizontally extending formations or formations dipping at substantial angles from the horizontal. However, it is not effective in areas with near vertical boundaries or with boundaries located beneath a formation which obscures the boundary from surface emanating seismic waves.
U.S. Pat. Nos. 1,909,205 McCollum, 2,021,943 McCollum, 2,813,590 McDonald and 3,483,505 Adair et al describe apparatus and methods for logging vertical formations from a borehole with a logging sonde. In these patents, acoustic energy from a single source strikes the vertical formation at various angles dependent upon the location of the source with respect to the attitude of the formation. The reflected acoustic energy is detected at detectors spaced a substantial distance from the source.
U.S. patent applications, Ser. No. 669,077, filed Mar. 22, 1976, Ruehle, Ser. No. 844,550, filed Oct. 25, 1977, Ruehle and Ser. No. 793,680, filed May 4, 1977, now U.S. Pat. No. 4,146,870, Ruehle describe and claim methods of marine seismic exploration wherein directivity of acoustic pulses emanating from a linear array of sources and directivity of a linear array of receivers is obtained.